The present invention relates to a system and method for use in the continuous monitoring of the structural integrity of a component or structure and in particular for monitoring the integrity of a structure or component to provide an early indication and location of an impending flaw such as a fault or crack and to monitor the growth of the fault or crack.
A very important function of design and maintenance engineers is to monitor for, locate and assess the initial location of surface faults or cracks that develop in structures or components under static or dynamic loads and subsequently determine the likely propagation path and rate of growth of the fault or crack. Examples where the monitoring of surface faults and cracks may be critical include on wing sections of aircraft; turbine blades on jet engines, the hull of a ship and the boiler of a nuclear power plant. Often, the monitoring is by visual inspection only. However it will be appreciated that when faults or cracks initially develop they are often extremely small and imperceptible to the eye. Alternately, the faults or cracks may arise in structures or components that are physically difficult or indeed impossible to access.
A system to measure microscopic crack growth rate must have high sensitivity. International Application No PCT/AU94/00325 (WO 94/27130) in the name of Tulip Bay discloses a monitoring apparatus that can be used to detect faults or cracks in the surface of a structure. The monitoring apparatus described includes a substantially constant vacuum source connected in series with a high impedance to fluid flow device that in turn is connected with one or more minuscule flaw sensing cavities formed on the surface of a structure. A differential pressure transducer is connected across the high impedance to fluid flow device to monitor the vacuum state of the minuscule flaw sensing cavity or cavities relative to the constant vacuum source. Accordingly, if there is a change in vacuum condition in the cavities which can arise from the formation and propagation of a crack, the change is detected by the transducer. With this method, cracks of a length down to 250 micron have been detected using a constant vacuum source of only 20 kPa below atmospheric reference. Upon initial indication, minuscule increase in crack growth can be detected. Embodiments of the present device and method are suited for use with the monitoring apparatus described in the aforementioned International application.
Oertle in (U.S. Pat. No. 4,145,915) and (U.S. Pat. No. 4,109,906) claims early crack detection but lacks the sensitivity and practicality to carry out the proposed tasks. This arises because in Oertle, the whole vacuum system volume forms part of a flaw sensing cavity and therefore relatively high vacuum must be employed in order to provide some sensitivity to the method. This becomes obvious if a constant vacuum source of only 20 kPa below atmospheric reference were to be used by Oertle. Further, the use of high vacuum dictates the use of low permeability materials which limits practical application.
Tulip Bay (WO 94/27130) has the advantage that the flaw sensing cavity is, to a large extent, isolated from the vacuum source and can therefore be of minuscule volumetric capacity.
Objects of the present invention include: to provide a system and method for continuous monitoring of a structure or component to provide an early indication and location of an impending fault or crack; and, to monitor the growth of the fault or crack.
For ease of description from hereinafter, including the claims, the term xe2x80x9cstructurexe2x80x9d is used as a reference to a structure or component.
According to the present invention there is provided a system for use in the continuous monitoring of the structural integrity of a structure, said system including at least:
an elastomeric sensor pad having a first structure engaging surface and an opposite surface, said first structure engaging surface provided with a set of at least one first channels which, when said first structure engaging surface is sealingly engaged with said structure, form a corresponding set of at least one first cavities;
first fluid communication means for providing fluid communication between said set of at least one first channels and a constant vacuum source; and
isolation means for isolating each of said first cavities from fluid communication with said constant vacuum source.
Preferably said system further includes means for monitoring for a variation in the vacuum condition between the constant vacuum source and said first cavities.
In one embodiment, said sensor pad further includes:
a set of at least one second channels formed on said first structure engaging surface which, when said first surface is sealingly engaged with said structure, form a corresponding set of at least one second cavities;
said second channels intersperse with said first channels; and,
a second fluid communication means for providing fluid communication between said second cavities and an atmosphere or environment at a pressure different to said constant vacuum source.
Preferably said first communication means includes a third channel provided in said first surface, said third channel being in fluid communication with each of said first channels and with said constant vacuum source.
In an alternate embodiment said first fluid communication means includes a plurality of conduits, one of each providing fluid communication between respective first channels and the constant vacuum source.
Preferably said second communication means includes a fourth channel provided in the first surface, said fourth channel being in fluid communication with each of said second channels and said atmosphere or environment.
Preferably a said sensor pad is transparent or at least translucent.
Preferably the system further includes a supply of a dye indicating liquid in fluid communication with said second channels to provide a visual indication of the location of a flaw.
In an alternate embodiment said second fluid communication means comprises an opening in each of said first channels that provides fluid communication through the pad to said atmosphere environment.
Preferably said isolation means includes means for applying force to said pad at respective locations above each or selected ones of said first and/or second channels, to seal said first and/or second channels against the structure and fluidly isolate said first and/or second cavities from said vacuum source.
Preferably said isolating means is adapted to individually and/or sequentially isolate said cavities so that progressively all of said cavities are isolated from said vacuum source.
Preferably said isolating means is programmable so that the sequence of isolating said cavities can be varied.
In one embodiment, said means for applying force includes a plurality of actuators supported on or in said pad above each of said channels for applying force to sealingly deform said channel against the structure.
Preferably said actuators are electrically, magnetically, hydraulically, pneumatically, or mechanically operated.
Preferably said first communication means includes a duct formed on a second surface of said pad opposite said first surface and respective holes formed in said pad providing fluid communication between said first channels and said duct, and said isolation means includes means for applying a fluid isolation force at respective locations to obstruct said duct, to fluidly isolate selected ones of said first channels from said vacuum source.
Preferably said isolating means is adapted to individually and or sequentially isolate said cavities so that progressively all of said cavities are isolated from said vacuum source.
Preferably said isolating means is programmable so that the sequence of isolating said cavities can be varied.
In one embodiment, said means for applying force includes a plurality of actuators supported on or in said pad above each of said lengths for applying force to said pad to sealingly deform said corresponding channel against the structure.
Preferably said actuators are electrically, magnetically, hydraulically, pneumatically, or mechanically operated.
In a further embodiment, said means for applying a fluid isolation force includes a pair of minuscule pinch rollers disposed on opposite sides of said duct for sealing a length of said duct from said vacuum source to progressively isolate said first channels in communication with said length from said vacuum source.
In another embodiment, said means for applying a fluid isolation force includes a moveable seal disposed in said duct for sealing a length of said duct from said vacuum source and means for moving said seal along said duct to progressively fluidly isolate said first channels in communication with said length of said duct from said vacuum source.
In a still further embodiment, said channels extend in a radial direction.
According to the present invention there is also provided a method for continuously monitoring the integrity of a structure, said method including at least the steps of:
providing a sensor pad having a first structure engaging surface and opposite surface, the first surface provided with a set of at least one first channels;
sealingly engaging said first surface of the sensor pad with the structure so that said channels together with the structure form a corresponding set of first cavities;
coupling said first cavities to a constant vacuum source;
monitoring for a change in vacuum condition between said cavities and said constant vacuum source; and
isolating each of said first cavities from said constant vacuum source.
In one embodiment, the step of isolating each of said first cavities includes venting said first cavities to the atmosphere or surrounding environment.
According to the present invention there is also provided a method for continuously monitoring the integrity of a structure, said method including at least the steps of:
providing a sensor pad having a first structure engaging surface and an opposite surface, the first surface provided with a set of at least first channels and a set of at least one second channels, said first channels isolated from and interspersed with said second channels;
sealingly engaging said first surface of the sensor pad to the structure so that said channels together with the structure form a corresponding set of first and second cavities;
coupling said first cavities to a constant vacuum source;
coupling said second cavities to an atmosphere or environment at a different pressure or vacuum condition to said constant vacuum source;
monitoring for a change the vacuum condition between said first cavities and said vacuum source; and
isolating each of said first cavities from said constant vacuum source.
Preferably said step of isolating said cavities includes individually and sequentially isolating said cavities so that progressively all of said cavities are isolated from said vacuum source.
Preferably said method further includes forming said pad of a transparent or translucent material.
Preferably said method further includes the step of placing a supply of a dye indicating liquid in fluid communication with said second channels to provide a visual indication of the location of a flaw.